Macroscopic examination

micro-morphology analysis

metallographic examination

Brinell hardness and micro-Vickers hardness test were carried out for the fillet weld of the steam turbine high pressure inner cylinder drain pipe. The results showed that there were continuous incomplete penetration defects at the root of the fillet weld between the drain tube and the cylinder block

and the Brinell hardness and local microhardness of weld

heat affected zone were high

especially near the fracture surface of weld generally higher

the microhardness at the abrupt change of weld shape in the impermeable position was the highest

where the main crack originated. The reason for the fracture of the drain pipe was the improper welding control

continuous incomplete penetration defects were occurred at the root of fillet weld

which leaded to stress concentration. Under the long-term high temperature environment and high circumferential stress

the crack initiated at the abrupt change of the weld shape in the incomplete penetration position and extended to the outer wall and circumferential direction

resulting in the fracture failure of the joint. Attaching importance to and controlling welding quality and taking effective measures to eliminate welding residual stress was the key to avoid such problems. The analysis results of this paper are of great significance to the safe operation of power station steam turbine.